The present invention relates to printers and more specifically to a method for operating a printer with non-integer scaling of raster images with print quality enhancement.
Images representing font characters may be stored in what is known as bitmaps. As the name suggests, a bitmap is a mapping of ones and zeroes which indicates the color values that individual picture elements or "pels" within an image will have when displayed by an output device. For example, a value of "1" within a bitmap may indicate that a corresponding picture element will have a color value of black when the image is printed on a black and white printer. A value of "0" may indicate that a corresponding picture element has a color value of white when the image is printed. Some users of printers have print jobs with old font resources, wherein the resolution is, for example, 240 pels per inch. New printers may have resolutions of 300-600 pels per inch. Thus, there is a need for a method and system for scaling images with a resolution of 240 pels per inch to 300 or 600 pels per inch. This problem is not limited to the precise image resolutions mentioned herein, it occurs continually as printer image resolution improves.
A method for enhancement based on matches of image features is described in U.S. Pat. No. 4,437,122, which is incorporated by reference. This patent describes a method of enhancing the resolution and quality of characters. The method involves identifying patterns or "neighbor fields" surrounding selected pels within an input set of pels and enhancing the selected pels based on the features of the surrounding "neighbor field." The process results in a character whose resolution has been increased by a factor of three and whose diagonal and curved strokes have been smoothed.
Another patent in the same technical area is U.S. Pat. No. 5,387,985 which is also incorporated by reference. This patent relates to the use of a plurality of lookup tables wherein each lookup table represents a unique phase relationship between the input and output bitmaps and to the use of an intermediate bitmap with a resolution that is a common multiple of the input and output resolutions to effect non-integer resolution conversion.
However, the prior art is believed to lack the flexibility required for solving the problems of users of printers who have print jobs with old font resources and require non-integer scaling of font characters with quality enhancement.